Switching the Enantioselectivity in Catalytic [4 + 1] Cycloadditions by Changing the Metal Center: Principles of Inverting the Stereochemical Preference of an Asymmetric Catalysis Revealed by DFT Calculations.
The mechanisms of the asymmetric [4 + 1] carbocyclization of vinylallenes with carbon monoxide catalyzed by Pt(0) and Rh(I) carrying the chiral support ligand (R,R)-Me-DuPHOS (Me-DuPHOS = l,2-bis(2,5- dimethylphosphorano)benzene) were studied using density functional theoretical models. Previously,...
| Publicado en: | Journal of the American Chemical Society Vol. 136; no. 26; pp. 9414 - 9424 |
|---|---|
| Autores principales: | , , , |
| Formato: | Artículo |
| Publicado: |
American Chemical Society
7/2/2014
|
| Materias: | |
| Acceso en línea: | Ver este registro en EBSCOhost |
| fields | @attributes: recordID: 1 pdfLink: plink: https://search.ebscohost.com/login.aspx?direct=true&db=hlh&AN=97473441&site=ehost-live header: @attributes: shortDbName: hlh uiTerm: 97473441 longDbName: Humanities International Complete uiTag: AN controlInfo: bkinfo: jinfo: jid: 00027863 ACS jtl: Journal of the American Chemical Society issn: 00027863 maglogo: N pubinfo: dt: 7/2/2014 vid: 136 iid: 26 pid: 997 pub: American Chemical Society artinfo: ui: 97473441 10.1021/ja503427f ppf: 9414 ppct: 10 formats: tig: atl: Switching the Enantioselectivity in Catalytic [4 + 1] Cycloadditions by Changing the Metal Center: Principles of Inverting the Stereochemical Preference of an Asymmetric Catalysis Revealed by DFT Calculations. aug: au: Mazumder, Shivnath Crandell, Douglas W. Lord, Richard L. Mu-Hyun Baik affil: Department of Chemistry, Indiana University, 800 E. Kirkwood Avenue, Bloomington, Indiana 47405, United States Department of Chemistry, Grand Valley State University, 1 Campus Drive, Allendale, Michigan 49401, United States Department of Materials Chemistry, Korea University, Jochiwon-eup, Sejong-si, 339-700, South Korea su: Enantioselective catalysis Ring formation (Chemistry) Asymmetry (Chemistry) Carbon monoxide Density functional theory Enantiomers Platinum catalysts Rhodium catalysts sug: subj: Enantioselective catalysis Ring formation (Chemistry) Asymmetry (Chemistry) Carbon monoxide Density functional theory Enantiomers Platinum catalysts Rhodium catalysts ab: The mechanisms of the asymmetric [4 + 1] carbocyclization of vinylallenes with carbon monoxide catalyzed by Pt(0) and Rh(I) carrying the chiral support ligand (R,R)-Me-DuPHOS (Me-DuPHOS = l,2-bis(2,5- dimethylphosphorano)benzene) were studied using density functional theoretical models. Previously, it was observed that the (R)-stereoisomer of the 5-substituted 2-alkylidene-3- cyclopentenone products was obtained with Pt(0), but the (S)-enantiomer was formed when Rh(I) metal was used to promote the reaction. Our calculations suggest that the ratedetermining step in both cases consists of a C—C coupling between the vinyl end of the vinylallene substrate and carbon monoxide that is accompanied by charge transfer from the metal center to the organic substrate. The reason that the two metals give different enantiomer products lies in the very different geometries of the metal centers in the transition state. The platinum center adopts a square-planar geometry throughout the C—C coupling reaction, which forces the carbonyl to migrate from the metastable, pseudoaxial position into the equatorial plane. During this migration, the carbonyl encounters the spatial constraints caused by the asymmetric DuPHOS ligand, while the vinylallene fragment is pushed away from the metal center. Thus, regardless of the steric demands of the organic substrate, the transition state that places the vinyl in a position that allows the CO to move into the sterically less crowded side of the molecule is preferred. Rh, on the other hand, maintains a square-pyramidal geometry throughout the reaction, keeping the CO ligand at the axial coordination site. The C—C coupling is accomplished by pulling the vinylallene substate closer to the metal and, as a result, the transition state that causes the least amount of steric clashes between the substrate and the DuPHOS ligand is favored, which affords the (S)-enantiomeric product. pubtype: Academic Journal doctype: Article src: R language: English refInfo: copyright: @attributes: flag: Y dt: @attributes: year: 2014 holdings: @attributes: islocal: N |
|---|